1. Field of the Invention
The present invention relates to a flat fluorescent lamp, and more particularly to, a flat fluorescent lamp with improved discharge efficiency which improves discharge efficiency and luminance with an increase of a current density of discharge channels by forming multiple discharge channels of an independent serpentine layout and an exhaust channel, reduces a firing potential with the enhancement of an electrode structure and eliminates non-light emitting regions caused from an external electrode with the design of electrode spaces having a width larger than the discharge channels.
2. Description of the Background Art
In a liquid crystal display (LCD), which is a passive type one of flat panel displays, a backlight unit as a light source, includes a cold cathode fluorescent lamp (CCFL), an external electrode fluorescent lamp (EEFL), an external internal electrode fluorescent lamp (EIFL), a flat fluorescent lamp (FFL), an electro luminescence (EL), a light emitting diode (LED) and the like. Among them, the CCFL is widely used in thin film transistor liquid crystal displays (TFT LCDs) since the CCFL has a long life, low power consumption, and is commercialized.
The CCFL type can be categorized into a direct type and an edge light type. Of them, the direct type CCFL is problematic in that the use of tens of lamps makes it difficult to acquire the reliability of the lamp of a liquid crystal display, and decreases the economic efficiency depending on an increase of an assembly unit cost. The edge type CCFL has a limitation in luminescence required for a large-sized liquid crystal display panel since a light is emitted from the end portions.
Therefore, the utilization of a flat fluorescent lamp (FFL) as a backlight unit is being positively examined. The flat fluorescent lamp satisfies both luminescence and lamp reliability, enhances optical efficiency and reduces the production cost of a liquid crystal display.
The flat fluorescent lamp is mostly divided into a CCFL type and an EEFL type according to the arrangement of electrodes.
Every discharge channels of the CCFL type flat fluorescent lamp is divided by a partition and extends to a serpentine layout channel. The starting region of the discharge channel is disposed in opposite of the ending region, and a phosphor layer is coated in the long discharge channel.
The above-described conventional CCFL type flat fluorescent lamp requires a high firing potential in proportion to the length of a discharge channel since it has a long discharge channel. In other words, the CCFL type flat fluorescent flat fluorescent lamp needs a high voltage of tens of kilovolts for lighting. Accordingly, the output voltage of an inverter is increased, and a power loss can be occurred due to an electromagnetic wave failure phenomenon and a leakage voltage. Therefore, in a case that the CCFL type flat fluorescent lamp is employed as a backlight unit, it is hard to use the liquid crystal display for home use.
To eliminate the above-said disadvantages, a method of dividing a discharge channel into a plurality of ones may be proposed. In this case, however, it is difficult to smoothly solve the problem of exhaustion for an individual discharge space, and there occurs an additional problem that respective inverters have to be connected to divided discharge channels, thereby increasing the manufacturing cost.
On the other hand, in the EEFL type flat fluorescent lamp, electrodes are located only on the outer parts of both ends of a glass substrate on which discharge channels are formed, and thus discharging is done within a relatively short distance as compared to the CCFL type. Hence, the EEFL type flat fluorescent lamp enables discharging even at a low voltage to achieve a stable discharging. Further, the EEFL type flat fluorescent lamp is very convenient to install electrodes.
However, the EEFL type flat fluorescent lamp has a demerit that a desired luminescence can be obtained by acquiring a wide electrode area in order to flow a sufficient current with the use of an external electrode. Thus, the dead space of the lamp becomes larger to deteriorate the outer appearance of the lamp.
Besides, in the EEFL type flat fluorescent lamp, a plurality of discharge channels in a transverse direction is embodied. Thus, there arouses a problem that an excessive power is consumed for getting a proper current density for respective discharge channels.
Further, in a case that the cross sectional area of a discharge channel is reduced for getting a proper current density in the EEFL type flat fluorescent lamp, the number of discharge channels is increased and the width of a partition is increased too. This increase of the number of discharge channels increases power consumption, and this increase of the width of a partition brings about a larger dark portion by the partition. Besides, there occurs an additional problem that the thickness of a backlight unit is increased to overcome the dark portion problem.
The present inventor has made many attempts to solve the problem of the deterioration of the efficiency of the above-described planar discharge type flat fluorescent lamp. As a result, the present inventor applied for the techniques involved with flat fluorescent lamps such as Korea Laid-Open Patent No. 2002-0072260 (Sep. 14, 2002) ‘lamp assembly utilizing flat fluorescent lamp’, Korean Laid-Open Patent No. 2004-14037 (Feb. 14, 2004) ‘flat fluorescent lamp and lamp assembly using the same’, Korea Laid-Open Patent No. 2004-0013020 (Feb. 11, 2004) ‘backlight unit utilizing flat fluorescent lamp’ and Korea Laid-Open Patent No. 2004-0004240 (Jan. 13, 2004) ‘flat fluorescent lamp and backlight unit utilizing the same’, and the present inventor suggested a method of improving the optical efficiency of a flat fluorescent lamp by enhancing the structure and arrangement of electrodes and acquiring luminance uniformity by minimizing a non-light emitting region.
With this series of research results, the present inventor devised a flat fluorescent lamp having a plurality of discharge channels of a serpentine layout and utilizing a particular exhaust channel. Further, the present inventor devised a flat fluorescent lamp with combined internal and external electrodes in order to maximize efficiency.
A fluorescent lamp utilizing a hybrid electrode was disclosed in Korea Patent Registration No. 0392181 (Jul. 8, 2003) ‘discharge lamp and backlight unit employing the same’. Referring to FIG. 6 of the Korean Patent Registration No. 0392181, a CCFL type lamp having a hybrid electrode is disclosed.
Further, another fluorescent lamp employing a hybrid electrode was disclosed in Korea Patent Registration No. 0399006 (Sep. 8, 2003) ‘hybrid discharge-type flat fluorescent lamp’, and the Korea Patent Registration NO. 0399006 discloses a flat fluorescent lamp with combined direct current type electrode and alternating current type electrode. By this, it is possible to solve the problem that it is difficult to perform a stable discharge control at a low luminance by the control of a current of a direct current discharge type electrode having a direct current flowing since a metal electrode is exposed to a discharge space and the problem that it is difficult to achieve a high luminance due to a low current of an alternating current discharge type electrode with a dielectric layer coated on both opposite ends.
However, in case of the flat fluorescent lamp with combined direct current type internal electrode and alternating current type external electrode as shown in FIG. 6 of the Korean Patent Registration No. 0399006, discharge channels partitioned by partitions are all connected at both opposite ends, there may arouse a serious crosstalk in which every channel gathers to one channel having a relatively low firing potential. This crosstalk phenomenon is caused from the characteristic that a discharge occurs well at a region with the lowest resistance.
Subsequently, the above-described conventional technique has a restriction on the manufacture of a large-scale lamp due to the demerit that it is difficult to implement a discharge in the entire discharge channels and also has a restriction on the enhancement of optical efficiency.